The present invention relates to an optical information storage and retrieval device for a card-type optical information storage medium and, in particular, to a device of such a type that controls the drive of a drive means of a conveyor mount or an optical head.
Prior Art
Cards have recently attracted attention as compact optical information storage media. A device of this type is arranged such that information is recorded along the longitudinal direction of a rectangular card, so that information can be recorded and retrieved by causing the card and an optical head to be moved relatively and linearly to and fro. For that reason, a linear motor is used as a drive means and the configuration is such that a control circuit controls motor drive currents in accordance with speed control signals.
An example of a prior art circuit configuration that provides this type of control is shown in FIG. 4. In this circuit, a D/A converter 22 shapes an analog signal in accordance with an output from a controller 21 and sends it to an inverting amplifier 23. An output of the inverting amplifier 23 is sent to a non-inverting input pin of an amplifier 24 and an inverting input pin of another amplifier 25, and a current is sent from these two amplifiers to a linear motor coil 26 as shown by the solid line or the broken line in the figure. A current flowing through the linear motor coil 26 is detected by a resistor 28 and is fed back to the input side of the inverting amplifier 23 via a differential amplifier 27. It is then superimposed on the output of the D/A converter 22 to provide feedback control of the amount of power sent to the linear motor coil 26. The amount of movement of a card conveyor mount 30 caused by the power sent to the linear motor is detected as movement of a linear scale 31 by a linear sensor 32, this is fed back to the controller 21 and is used for determining the amount of current to the linear motor coil 26.
The waveforms of signals, voltages, and currents at various parts of this circuit are as shown in FIG. 5. As shown in this figure, when the card conveyor mount 30 accelerates linearly, is held at a constant speed, and then decelerates linearly, as shown in FIG. 5 (a), the output voltage of the D/A converter 22 is divided into an acceleration region, a constant-speed region, and a deceleration region, as shown in FIG. 5 (b). One of the outputs of the amplifiers 24 and 25, which act in mutually opposite phase in response to the signal amplified by the inverting amplifier 23, similarities to the waveform of FIG. 5 (b) and the other is the mirror image thereof, as shown in FIGS. 5 (c) and (d).
Voltages of the same waveform as that of the output of the D/A converter 22 are applied to the linear motor coil 26, as shown in FIGS. 5 (e) and (f), and thus currents of the same waveform flow therethrough.
Problem To Be Solved By the Invention
In this manner, the control circuit is configured using amplifiers, and the waveform in each amplifier is continuously powered. As a result, there is a problem in that the amplifiers generate a great deal of heat so that the temperature within the information storage and retrieval device becomes quite high and thus the temperature within the apparatus into which the information storage and retrieval device is incorporated also rises.